The detonation of a conventional explosive charge within a body of water produces an expanding gas bubble which eventually reaches a maximum diameter and begins to collapse. In open water, a bubble so formed will upon collapse have a spherical shape, oscillate a few times and eventually rise to the water surface. If such bubble is formed just beneath a submerged target, upon collapse it is no longer spherical as it rises upwardly and inverts to internally form a water jet impacting on the bottom of the target. Conventional explosives may be utilized to produce gas bubbles for such bottom-up target attack, but are not generally effective for side-on or top-down attacks because horizontal and downward moving jets are difficult to generate as a result of target attraction alone.
Heretofore, explosive generation of water jets as target warheads involved gas bubbles having internal mass density that was uniform throughout. As a result, the flow field of the gas within the bubble during its collapse was irrotational. Improvements in jet induced target damage therefore focused on the composition of a homogeneous explosive so as to maximize bubble size.
According to published research papers of the inventor, the collapse of a spherical shaped bubble so as to form an upward moving jet is possible even without the presence of a target if motion internally of the bubble is accelerated by a rotational flow field within the bubble upon reaching maximum size. Such rotational flow within the bubble gas was shown to result from a non-homogeneous gas density distribution that is spherically symmetric, characterized by a minimum density at the center of the bubble which increases along a parabolic curve to a maximum value at the outer bubble surface.
As to the formation of non-homogeneous explosive charges by different layer material compositions, U.S. Pat. Nos. 3,474,732 and 3,897,728 to Thomison and Stemberg et al. are of interest. However, the foregoing patents do not relate to bubble collapsing water jets or conditions affecting generation of such water jets. The Thomison patent relates instead to ignition of a massive magnesium structure by the layered explosive, while the Sternberg et al. patent relates to differential detonation of a layered explosive to enhance damage to an underwater target by shock waves.
It is therefore an important object of the present invention to enhance underwater target damage by impact of waterjets emerging from collapsing gas bubbles produced by detonation of non-homogeneous explosive charges.
It is an additional object of the invention to modify distribution of explosion product density within a bubble formed underwater by explosive charge detonation, so as to maximize target damage by the water jet resulting from bubble collapse upon reaching its maximum size.